Many lighting control network systems, including wireless lighting control systems and wired lighting control systems, include both an Ambient Light Sensor (ALS) and an occupancy detector. In a DALI (Digital Addressable Lighting Interface) system, for example, an ALS may be coupled to the bus as a first sensor node and an occupancy detector may be coupled to the bus as a second sensor node. The occupancy detector may be a PIR (Passive InfraRed) sensor. The presence of a person may also be detected in other ways. To conserve electrical energy, if no person is detected to be present in an area, then electrical lamps in the area are turned off and remain off. If, however, a person is detected to be present in the area, then artificial illumination is provided by the lamps as necessary. Many systems have the ability to vary the amount of artificial light provided. Conventional dimmers used with incandescent bulbs may be remotely controlled. Dimmable ballasts can be used to dim fluorescent lamps. If many lamps are used to illuminate an area, then some of the lamps can be turned off and others turned on such that the overall amount of artificial light provided is adjustable. Regardless of how the adjustment of the amount of artificial light is performed, the ALS sensor is typically used to detect the overall amount of ambient light and control how much artificial light is provided so that more artificial illumination than is needed is not provided. This is sometimes referred to as “daylight harvesting”. For example, if the area with full artificial light illumination would have a brightness that exceeds the desired brightness level, then the system does not illuminate the area with full artificial illumination but rather uses a lesser amount of artificial illumination such that the overall brightness (due to any natural light as well as due to artificial light) is not greater than necessary. As the amount of background natural light changes, so too does the proper amount of artificial light change. The ALS sensor provides ambient light measurement data to the system so that the system can vary the amount of artificial light.
There are many different types of lighting control systems that have these general characteristics. In one type of system, there are two brightness thresholds: an upper threshold, and a lower threshold. If the detected brightness is initially between the two thresholds and then transitions to be below the lower threshold, then an action of turning the lamps on to their maximum brightness is taken. If the detected brightness is initially between the two thresholds and then transitions to be above the upper threshold, then an action of dimming the lamps is taken. The system works well, but the setting of the thresholds can be difficult. Because a person manually adjusts the two thresholds, the spread between the two thresholds is also manually adjusted and can be set improperly. In adjusting a threshold, the user may obtain no visible feedback from the system. How much the threshold is being changed is therefore difficult to determine. The person may have to climb a ladder to interact manually with an adjustable system component multiple times. The person may have to watch and monitor the system, adjusting it several times before the system is suitably calibrated for its particular environment and particular configuration.
U.S. Pat. No. 7,608,807 describes a problem of a person who is commissioning a system having to monitor the system over a long period of time in order to calibrate the system properly. There is also another problem in a two threshold system. The thresholds can be set such that the system oscillates between illumination settings. Despite these problems with manual adjustment, the flexibility of manual adjustment is provided because the thresholds may depend on many factors. System performance may, for example, depend on the structure of the building in which the system is installed, the contents of the building, the time of year and day, the types of artificial lighting used, and the number of lamps ganged together. As lamps burn out, lamps having different characteristics may be used as replacements and lighting system performance may change. Mechanisms for auto-calibrating ALS thresholds in such lighting systems are known, but these mechanisms are generally slow, semi-nonfunctional, undesirably complex, cumbersome and/or expensive.